1. Field of the Invention
The present invention relates to a voltage level shifting circuit for amplifying the voltage of a signal of the ECL level or other small voltage amplitude to change it to a signal of a large amplitude.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a first example of the configuration of a conventional voltage level shifting circuit.
This voltage level shifting circuit 10 is configured as a flipflop circuit comprised of a first inverter including a resistor 1 and an n-channel MOS transistor 7 connected at one end and a drain thereof, respectively, and a second invertor including a resistor 2 and an n-channel MOS transistor 8 connected at one end and a drain thereof, respectively, with the inputs and the outputs of the inverters connected cross-wise.
More specifically, a connection point between one end of the resistor 1 forming the output of the first inverter and the drain of the n-channel MOS transistor 7 is connected with the gate of the n-MOS transistor 8 forming the input of the second inverter, while a connection point between one end of the resistor 2 forming the output of the second inverter and the drain of the n-channel MOS transistor 8 is connected with the gate of the n-channel MOS transistor 7 forming the input of the first inverter.
Also, input terminals 3 and 4 are constituted by the connection points with the supply lines of the power supply voltage of the inverters, that is, the other ends of the resistors 1 and 2. A variable power supply voltage is input to the input terminals 3 and 4 as the input signals V.sub.in1 and V.sub.in2.
The flipflop of the voltage level shifting circuit constituted in this way, as shown in FIG. 2, has two stabilization points a and b in the case where the input signals V.sub.in1 and V.sub.in2 are the same level.
Further, by giving a slight amplitude difference .DELTA.V.sub.in between the input signals V.sub.in1 and V.sub.in2, the flipflop is made unstable in a state as shown by the broken line of FIG. 2. If there is only one stabilization point, that is, the point shown by c, the operation point shifts to that stabilization point c.
By reversing the stabilization point of the flipflop by a slight change of the input voltage, a large output amplitude can be obtained.
FIG. 3 is a circuit diagram of a second example of the configuration of a conventional voltage level shifting circuit, while FIG. 4 shows the output characteristics of the circuit of FIG. 3.
This circuit uses the p-channel MOS transistors 24 and 23 instead of the n-channel MOS transistors of FIG. 1 and the positions of the MOS transistors and the resistors 21 and 22 are reversed.
In this case too, variable power supply voltages are used as the input signals. The basic operation, like with that of the circuit of FIG. 1, is one which uses a slight amplitude difference .DELTA.V.sub.in between the input signals V.sub.in1b and V.sub.in2b and reverses the stabilization point of the flipflop to obtain a large output amplitude.
FIG. 5 is a circuit diagram of a third example of the configuration of a conventional voltage level shifting circuit, while FIG. 6 shows the output characteristics (butterfly-plots) of the circuit of FIG. 5.
This circuit uses the p-channel MOS transistors 41 and 42 as loads instead of the load resistors of FIG. 1 and connects the gates of the p-channel MOS transistors 41 and 42 to the input terminals 45 and 46.
The basic operation is similar to that of the circuit of FIG. 1 and FIG. 2. A slight amplitude difference .DELTA.V.sub.in between the input signals V.sub.in1b and V.sub.in2b is used to reverse the stabilization point of the flipflop to obtain a large output amplitude.
However, in the above-mentioned conventional circuits, direct current (DC) is consumed, so it is necessary to increase the DC current in order to increase the drive capacity.
Further, to invert: the output, a certain magnitude of input amplitude is required. Further, there is the problem that the output amplitude is not a full swing one.